#include <bits/stdc++.h>


using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");

const int lmt = 1e5+1;

int n,m,id,ids[lmt], low[lmt], stccCount;
vector<int> aList[lmt], rsp[lmt];
stack<int> stacc;
bool on_stacc[lmt];

void dfs(int nod)
{
    on_stacc[nod]=1;
    ids[nod]=low[nod]=++id;
    stacc.push(nod);

    vector<int>::iterator i;
    for(i=aList[nod].begin();i!=aList[nod].end();++i)
    {
        if(!ids[*i])
            dfs(*i);
        if(on_stacc[*i])
            low[nod]=min(low[nod], low[*i]);
    }
    if(low[nod]==ids[nod])
    {
        ++stccCount;
        while(!stacc.empty())
        {
            int poz = stacc.top();
            on_stacc[stacc.top()]=0;
            stacc.pop();

            if(poz==nod)
                break;
        }
    }
}

int main()
{
    fin>>n>>m;
    for(int i=1;i<=m;++i)
    {
        int x,y;
        fin>>x>>y;
        aList[x].push_back(y);
        sort(aList[x].begin(),aList[x].end());
    }
    for(int i=1;i<=n;++i)
    {
        if(!ids[i])
            dfs(i);
    }
    fout<<stccCount<<'\n';
    for(int i=1;i<=n;++i)
    {
        rsp[low[i]].push_back(i);
    }
    for(int i=1;i<=n;++i)
    {
        if(rsp[i].empty())continue;

        vector<int>::iterator j;
        for(j=rsp[i].begin();j!=rsp[i].end();++j)
            fout<<*j<<' ';

        fout<<'\n';
    }

    return 0;
}